Voltage limiting means



Nov. 7, 1950 c. H. sMooT I VOLTAGE LIMITING MEANS Filed Nov. 9, 1948 www. r

Patented Nov. 7, 1950 UNITED STATES PATENT OFFICE VOLTAGE LIMITING MEANS Charles Smoot, Chicago Ill., assigner to Republic Flow Meters Company, Chicago, Ill., a corporation of Illinois Application November 9, 1948, Serial No. 59,061

12 Claims. l

1This invention relates to voltage limiting means and more particularly tomeans for limiting either the maximum voltage, the minimum voltage, or both in a circuit.

It is desirable under many circumstances to limit either the maximum or the minimum voltage or both which is supplied to electrical units in either A. C. or D. C. apparatus.A In A. C. circuits it is also highly desirable to limit the voltage without distorting the waveform as occurs when ordinary clipping devices are employed. It is accordingly a principal object of the present invention to provide voltage limiting means which can limit either the maximum or the minimum voltage or both and which will not distort the Wave form of an alternating current voltage.v

Another object is to provide Voltage limiting means in which similar limiting devices can be utilized to limit both maximum and minimum voltage. To limit minimum voltage according to the invention, an external voltage is supplied to the circuit which is opposite in phase or polarity to the voltage to be limited and which is of greater amplitude so that the polarity or phase of the controlled voltage will be reversed. The maximum amplitude of the reversed voltage `is then limited, and subsequent to the limiting a second external voltage of the same amplitude as and of opposite phase or polarity to the rst external voltage is added.

The above and other objects and advantages of the invention will be more readily apparent when read in connection with the accompanying drawing, in which- Figure l is a diagrammatic view of one type of voltage limiting circuit, and the output from the circuit is from terminals l2 and I 3. Adjacent the terminal I0 there is illustrated a resistor I4 offering a relatively high impedance in the circuit. It will be understood that when a high impedance source is employed the resistor I4 may represent the source impedance, but when a low impedance source'is employed, a separate resistor, as shown, may be required.

Immediately after the resistor |4- and across the circuit there is connected a maximum voltl applied to the terminals I9 and Il.

Nage limiting device which, as shown in Figure 2,

,pair of parallel circuits indicated at I5 and I6 connected across the voltage limiting circuit. The circuit I5 includes a rectifier Il in series with a resistor I8 whose value is low relative to the resistor I4 with the rectifier I'I arranged to pass current downwardly from the line Ill-I2 to the line H-i3. The circuit I6 includes arectier I9 in series with a resistor 2| with the rectier I9 arranged so that its polarity isopposite to that of the rectier I5 to pass current from the line I lwl to the line lil-I2.

An alternating current source illustrated as a transformer 22 is supplied With alternating voltage from any convenient source of the same frequency and in phase With the signal source The secondary of the transformer is connected at vone side tothe line II--IS and has its other side also connected to this line through a potentiometer resistance 23. An adjustable Wiper 2:3 engages the resistance 23 and is connected through a rectiner 25 to a point in the circuit I5 between the rectifier Il and the resistor IS. As shown, the rectifier 25 is arranged opposite to the rectifier Il' in the circuit to pass current from the wiper to the circuit I5. The wiper is also connected through a rectier 26 to a point in the circuit I6 between the rectier I9 and the resistor 2t. The rectier 26 is arranged so that its polarity is opposite to that of the rectifier I9 in the circuit to pass current from the circuit I6 toward the Wiper. Preferably, a voltmeter, as shown at 2l, is connected from the wiper to the line II-I3 to indicate the voltage for which the wiper is adjusted.

In operation assume that a voltage is impressed across the terminals It and H whose polarity is such that the terminal iii is positive relative to the terminal Il. A similar voltage in phase With the impressed voltage is supplied to the transformer 22, and the wiper 2t is adjusted to the maximum value of the impressed voltage desired. For example, the wiper 2t may beso adjusted that the voltage thereon is forty (40) volts positive relative to the line I I l 3. As long as the voltage on the terminal i@ is less than forty (40)' volts, there will be no now through either ofthe circuits I5 or It, the rectier Ill blocking flow through the circuit i6 and the forty (40) volt potential impressed on the mid point of the circuit I5 through the rectifier 'should Vexceed that between terminal 'El vwiper 24, current will flow from the terminal Il Vby adjustment of the wiper 24.

25 preventing any flow through the rectifier l1.

If, however, the potential on the terminal I should exceed that on the wiper 24, current will flow from the line lil-I2 through the rectifier l1 and resistor lil to the line ll-I3 to drop the potential across the two lines to that for which the wiper 24 is adjusted, Thus the peak voltage during the half cycles when the terminal ill is positive can never exceed that for which the wiper 24 is adjusted. Since the voltage on the terminal and the wiper are both sine wave voltages, it will be noted that the value at all positions on the wave is fixed by the instantaneous potential of the wiper 24 so that the voltage is limited according to a sine wave and is not distorted.

When the polarity is reversed so that terminal II is positive relative to terminal lil, the wiper 24 becomes negative relative to the terminal Il. As long as the wiper 24 is more negative than terminal I0 relative toterminal ll, there will b e 'noilow through the rectifier I9, but a flow will be established around the local circuit including the wiper 24,l the resistor 2l, and the rectifier Y26 to maintain the potential at the mid point of the circuit l5 equal to that of the wiper 2li. If the potential across the terminals IB and ll and through the circuit i6 to the line lil-l2 to reduce the potential diiference to that established In this case also reduction ofthe potential will follow the wave form of the potential on the wiper 24 so that the wave will be undistorted. The voltmeter 21 serves to indicate adjustment of the wiper.

To limit the minimum voltage in the circuit, a second maximum voltage limiting vdevice is connected across the circuit spaced from the first described device. As shown in Figure 2, the second maximum voltage limiting device is identical with the first maximum voltage limiting device and parts thereof are indicated by the same reference numerals plus Hifi. Between the two maximum voltage limiting devices a voltage is supplied to the circuit which is greater in amplitude than the maximum for which the rst limiting device is set and which is 183 out of phase with the input voltage. As shown, this voltage is supplied by a' transformer 33 whose secondary is connected in series in the line l-IZ and whose primary is supplied from alternating current sources equal in frequency and in phase with the supply source. The transformer is so wound and connected that the secondary voltage is out of phase with the impressed voltage and is in excess of the value for which the rst limiting device is set. For example, if the rst limiting device is set for forty (40) volts, the transformer 3G may impress forty-five (45) volts on the circuit.

The effect of the transformer 33 is illustrated diagrammatically in Figure 3 wherein the dotdash line 3| represents the output voltage from the first limiting device and the dotted line 32 indicates the voltage wave of the transformer secondary. These two voltages will be added algebraically to produce an output voltage wave indicated by the solid line 33 which is of opposite phase to the wave 3i and whose amplitude is equal to the algebraic sum of the waves 3l and 32. It will be noted that as the wave 3l becomes smaller in amplitude, the wave 33 increases in amplitude.

The wave 33 is impressed across the second voltage limiting device which functions in exactly the same manner as the first voltage limiting device to limit maximum voltage of the wave 33. If the wave 33 should tend to exceed the Value for which the second voltage limiting device is set, its amplitude will be reduced without producing distortion of its wave form. Thus the output wave from the second voltage limiting device which is inverted in phase with respect to the impressed wave can never exceed a predetermined amplitude.

Following the second voltage limiting device a second transformer 34 is connected in the line Ill-l2 to supply thereto a voltage wave equal in amplitude to'the voltage supplied by the transformer 33 but again inverted in phase so that it is in phase with the initially impressed wave. The effect of this transformer is illustrated in Figure e wherein the dot-dash line 35 indicates the voltage wave at theoutput side of the second limiting device and the dotted line 36 indicates the voltage wave produced by the transformer 34. It will be noted that these two voltages are out of phase so that they `will be added algebraically to produce the resultant output wave 31. It will be seen that this wave is equal in phase and amplitude to the wave 3l as seen in Figures 3 and 4.

When the output wave from the first limiting device, as shown at 3l, is in excess of the desired minimum value, the conditions, as illustrated in Figures 3 and 4, will exist. However, if the wave 3l should be below the desired minimum, it will be seen that when it is inverted and added to the wave 32 toproduce the wave 33 the amplitude of the wave 33 will be greater than the maximum value for which the second voltage limiting device is set. Under these conditions the second voltage limiting device will limit the voltage of the wave 33 so that when it is added algebraically to the voltage 36 the resultant output voltage 31 will at all times equal orv exceed a predetermined minimum value. It will further be noted that this is accomplished without distorting the wave form.

While the voltage limiting device as described may find many uses either for limiting maximum voltage or minimum voltage or both, there is illustrated in Figure l a control system in which the device is desirable. The system, as shown, is adapted to maintain e, predetermined fluid pressure in a conduit 38 supplied with fluid by a pair of blowers 39 and 40 driven respectively by motors 4| and 42. Flow through the conduit is controlled by a butterfly Valve 43 operated by a regulator 44 which may be of the type more particularly described and claimed in the patent to Rosenberger, No. 2,220,176. Such a regulator, as described in the Rosenbergerfpatenhwill function to produce a valve position proportionalto a loading pressure which in the construction illustrated is supplied by a solenoid 45 so that the valve .position will be proportional to the current flow through the solenoid 45.

In the construction shown the motor 42 is connected directly to a source 4B so that'it will run constantly during operation, andthe motor 4l is connected to the source through a switch 41 controlled bya solenoid 48. When the current in the solenoid 4,8 is less than a predetermined value, the switch 41 will beclosed, but when the current exceeds the predetermined value, the switch 41. will open to stop the motor 4l and the blower 39.

Pressure in the pipe 38 is sensed by a diaphragm 49 controlling a regulator 5| which may be of the type more particularly described and claimed in the patent to Rosenberger, No. 2,220,176. This regulator moves a Wiper 52 over a potentiometer resistance 53 to a position variable with the pressure in the pipe 38. The resistor 53 is supplied from a Source 54 of alternating current which may also supply the voltage limiting circuit indicated generally at 55. The terminals l and Il of the voltage limiting circuit are `connected across the wiper 52 and one side or" thc resistor 53 to receive a variable input voltage which is adjustable in accordance with the pressure in the pipe 38. The output terminals l2 and I3 of the voltage limiting circuit are connected to the coils 45 and 48, as shown.

The regulator i4 is so adjusted that when the current supplied to the coil 45 is relatively low the valve 43 will be open and as the current increases the valve will move toward its closed position. As the valve 43 is moved to a more nearly closed position to restrict flow through the conduit 38 thereby to reduce the pressure at the downstream side of the valve, the motor 4l will be cut out so that al1 of the fluid will be supplied by the single blower 40. On the other hand, as the valve starts to open, the moto-r 4I will be energized so that iiuid will be supplied by both of the blowers.

As the pressure changes in the pipe 38, the regulator 5l will adjust the wiper 52 to change the voltage supply to the coils 45 and 48 which are preferably so wound as to have a high impedance. If the voltage tends to exceed a desired maximum value, it will be limited by the rst voltage limiting device, as described above in connection with Figure 2, so that the maximum voltage applied to the coils can never exceed a predetermined value at which the valve 43 will be closed to its maximum closed position and the switch 47 Will be open. Similarly, the second voltage limiting device will prevent the voltage from ever falling below a predetermined minimum value which it is desired to maintain on the coils and particularly on the coil 45 to insure proper operation of the regulator 44. other uses for the voltage limitingr means of the invention can be found and that the system illustrated in Figure 1 is for example only.

While one embodiment of the invention has been shown and described in detail herein, it will be understood that this is illustrative only and is not to be taken as a denition of the scope of the invention, reference being had for this purpose to the appended claims.

What is claimed is:

1. A voltage limiting device for an alternating current circuit including two lines, comprising a pair of parallel circuits connected across the lines with a rectifier and an impedance in series in each circuit and with the polarities of the rectiers in the circuits opposite, an alternating current source of the same frequency as the voltage to be limited, and means connecting said source to points in the circuits between the rectiiiers and impedances in a phase relationship such as to oppose flow or" current between the lines through the circuits.

2. A voltage limiting device for an alternating current circuit including two lines, comprising a pair of parallel circuits connected across the lines with a rectier and an impedance in series in each circuit and with the polarities of the rectiers in the circuits opposite, an alternating current source of the same frequency as the voltage to be limited, and connections from the source It will be apparent that many gacross the impedances in a phase relationship suchV as to oppose flow of current between the lines through the circuits.

3. A voltage limiting device for an alternating current circuit including two lines, comprising a p-air of parallel circuits connected acrossthe lines with a rectier and an impedance in series in each circuit and with the polarities o the rectiiiers in the circuits opposite, an alternating current source of the same frequency as the voltage to be limited, separate connections from the source to points in the circuits between the rectiiiers and impedances, and rectiers in the connections of opposite polarity to the rectiers in the circuits.

4. A voltage limiting device for an alternating current circuit including two lines, comprising a pair of parallel circuits connected across the lines with a rectiiier and an impedance in series in each circuit and with the polarities of the rectiers in the circuits opposite, an alternating current source of the same frequency as the voltage to be limited, connections from the source across the impedances, and rectiers in the connections of opposite polarity to the rectiiiers in the respective circuits.

5. Avoltage limiting device for an alternating current circuit including two lines vcomprisinga pair of parallel circuits connected across the lines with a rectifier and an impedance in series in each circuitrand with the polarities of the rectiiiers in the circuits opposite, an alternating current source of the same frequency as the voltage to be limited, a connection from one side of the source to the line to which the impedances are connected, a resistor connected from the other side of the source to said line, a wiper engaging the last named resistor, separate connections from the wiper to points in the circuits between the rectiiers and resistors, and rectiers in the last named connections of opposite polarity to the rectifiers in the respective circuits.

6. A minimum voltage limiting circuit comprising a device for limiting maximum voltage connected across the circuit, a source to impress on the circuit at the input side of the device a predetermined voltage of opposite polarity than and larger than the maximum value of the voltage to be limited, and a second source to impress on the circuit at the output side of the device a, voltage equal to said predetermined voltage and of thev same polarity as the voltage to be limited.

7. A minimum voltage limiting means for an alternating current circuit comprising a device connected across the circuit to limit the maximum voltage thereacross, an alternating current source of opposite phase and of greater amplitude than the voltage to be limited connected in one side of the circuit at the input side of the device, and a second alternating current source of the same phase as the voltage to be limited and ci the same amplitude as the first named source connected in said one side of the circuit at the output side of the device.

8. Voltage limiting means for a circuit comprising a pair of maximum voltage limiting devices connected across the circuit at spaced points, a voltage source of greater amplitude than and of opposite polarity to the voltage to be measured connected in the circuit between the devices, and a second voltage source of the same amplitude as the first named source and of the same polarity as the voltage to be limited connected in the circuit at the output side of the devices.

9. Voltage limiting means for a circuit comprising a pair of maximum voltage limiting devices connected across the circuit at spaced points, a voltage source of greater amplitude than and of op-posite polarity to the voltage to be measured connected in the circuit between the devices, and a second voltage source of the same amplitude as the rst named source and of the same polarity as the voltage Yto be limited connected in the circuit at the output side of the devices, each of said devices including a rectiiler and a resistor in series connected across the circuit, and a voltage source of the same polarity as the volta/ge to be measured connected across the resistor.

l0. Voltage limiting means for an alternating current circuit comprising a pair of maximum voltage limiting devices connected across the circuit at spaced points, an alternating current source of greater amplitude than and opposite in phase to the Voltage to be limited connected in the circuit between the devices, and a second alternating currentsource of the same amplitude as and opposite in phase to the first named source connected in the circuit at the output side of the devices.

11. Voltage limiting means for an alternating current circuit comprising a pair of maximum voltage limiting devices connected across the circuit at spaced points, an alternating current source of greater amplitude than and opposite in phase to the voltage to be limited ccnnected in the circuit between the devices, and a second alternating current source of the same amplitude as and opposite in phase to the first named source connected in the circuit at the output side oi the devices, each of said devices including a pair of parallel circuits having a rectifier and a resistor in series with the rectiers inthe 'pair' of circuits oppositely connected, and an alternating current source of the same frequency'as thevoltage to be measured connected across the resistors in a phase relationship such as to oppose -ow oi current through the pair vof circuits.

12. Voltage limitingmeans for an alternating current circuit comprising a pair of maximum voltage limiting `devices connected across the circuit at spacedy points, an alternating current source of greater amplitude than and opposite in phase tothe voltage to bel limited connected in the circuit between the devices, and a second alternating current source of the same amplitude as and opposite in phase to the first named source connected in the circuit at the output side of the devices, each of said devices including a pair of parallel circuits having a rectifier and a resistor in series with the rectiiers in thel pair of circuits oppositely connected, an alternating current source of the same frequency as the voltage to be measured connected across the resistors in a phase relationship such as to oppose ilow of current through the pair oi circuits, and rectifiers between the last named source and the resistors of opposite polarity than the rectiiers inthe-respective circuits.

CHARLESH. SMOOT.

REFERENCES CITED 'The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,098,3'Z0 Bartels V Nov. 9, 1937 2,285,044 Morris June 2, 1942 

